1. Field of the Invention
This invention relates generally to a machine adapted to mill blanks to create filter lenses for a clip-on accessory which hitches onto the frame of prescription eyeglasses having a pair of optical lenses, the filter lenses then being in registration with the optical lenses to protect the wearer of these eyeglasses from harmful radiation. More particularly, the invention relates to a computer-controlled milling machine which produces filter lenses for a clip-on accessory whose geometry matches that of the frame of the eyeglasses.
2. Status of Prior Art
An individual who is myopic (near-sighted) or hyperopic (far-sighted), or suffers from other visual defects normally wears a pair of eyeglasses in which optical lenses are mounted in a frame having temple pieces hinged thereto. The optical lenses are designed to correct for the visual defects of the wearer and are therefore usually prescribed by an optometrist or an eye doctor.
The same individual may on occasion be exposed to harmful radiation, such as intense sunlight, rays from a welding arc or from a laser beam instrument. He therefore requires sunglasses or other radiation protection glasses whose filtration characteristics depend on the nature of the harmful radiation to which the wearer is exposed.
When an individual wearing prescription eyeglasses switches to a pair of sunglasses to protect his eyes from harmful radiation, it is essential that the filter lenses of these sunglasses have the same corrective optical properties as the optical lenses in his eyeglasses—otherwise he will not see clearly through his sunglasses. However, a pair of prescription sunglasses tailored to the eyes of its wearer is at least as expensive as a costly pair of prescription eyeglasses. Hence the wearer may be reluctant or unable to bear these additional costs.
To avoid the need for prescription sunglasses, the wearer of prescription eyeglasses can convert his eyeglasses to sunglasses simply by hitching onto the frame of his eyeglasses a clip-on accessory. This accessory is provided with a pair of filter lenses that register with the optical lenses of the eyeglasses to filter out harmful radiation.
The typical clip-on is a universal accessory in the sense that it is capable of being clipped onto the frame of a pair of prescription eyeglasses regardless of the geometry or design of this frame. This is a distinct advantage, for in this era of “designer” frames, eyeglasses are now marketed in a broad range of distinctly different styles.
The disadvantage of a universal clip-on accessory which may have discouraged its more widespread use is that the standardized design of a clip-on accessory includes round filter lenses. This design is usually incompatible with the frame design of the eyeglasses onto which the accessory is hitched. It is the frame of eyeglasses that impart to eyeglasses its overall appearance. Thus if the frame is composed of trapezoidally-shaped half-sections and the filter lenses of the clip-on accessory hitched thereon are circular, the appearance of the accessory is then incongruous and unappealing.
Hence while a clip-on accessory may be said to fit onto a pair of prescription eyeglasses, it would be more realistic to say that the clip-on accessory misfits these eyeglasses and renders them unattractive.
To obviate this drawback, there is disclosed in PCT patent publication WO 95/04634 “Clip-on Sunglasses and System for Cutting Clip-on Sunglasses” a machine to custom-cut the filter lenses of the clip-on accessory so as to impart thereto the same size and shape as the half-sections of the frame of the eyeglasses onto which the clip-on is hitched. To this end, the machine includes a holder for the eyeglasses to be copied and for the clip-on, and a cutter and stylus to trace the contours of the eyeglasses and to custom-cut the clip-on in accordance with this trace.
Also disclosing a method of customizing a clip-on accessory is PCT patent publication WO 93/24856 (1993). In this method, the pair of filter lenses for the clip-on have their perimeters cut to conform to the contours of a particular pair of eyeglasses. Of prior art interest is U.S. Pat. No. 5,546,140 to Underwood which discloses a machine for custom-cutting clip-on sunglasses, the machine trimming the sunglasses to conform to the shape and size of a pair of eyeglasses.